Conventionally, as a method for improving the corrosion resistance of aluminum or an aluminum alloy (hereinafter, aluminum or an aluminum alloy is also referred to as an aluminum-based material), an anodizing treatment has been conducted by which a porous anodic oxide film is formed on a surface of the aluminum-based material. In general, pores are arranged regularly in the porous layer of the anodic oxide film, although this greatly depends on the electrolysis conditions. This is a factor that causes decrease in corrosion resistance of the anodic oxide film.
In such a treatment, a sealing treatment for sealing the pores is conducted after the anodizing treatment for the improvement of corrosion resistance. An energy-saving sealing treatment has been proposed which is conducted at a lower temperature in a shorter time than a conventional high-temperature hydration type sealing treatment and which can provide corrosion resistance not inferior to the corrosion resistance provided by the high-temperature hydration type sealing treatment (Patent Document 1).